This invention relates to blends of a SAN polymer and a linear aromatic carboxylic polyester of monomer components consisting essentially of a bisphenol and a dicarboxylic acid wherein the dicarboxylic acid can be an aromatic dicarboxylic acid or an aliphatic saturated dicarboxylic acid such as oxalic or adipic acids.
Linear aromatic polyesters prepared from aromatic dicarboxylic acids and bisphenols are well known for their suitability for molding, extrusion, casting, and film-forming applications. For example, U.S. Pat. No. 3,216,970 to Conix, discloses linear aromatic polyesters prepared from isophthalic acid, terephthalic acid, and a bisphenolic compound. Such high molecular weight compositions are known to be useful in the preparation of various films and fibers. Further, these compositions, when molded into useful articles using conventional techniques, provide properties superior to articles molded from other linear polyester compositions. For instance, aromatic polyesters are known to have a variety of useful properties, such as good tensile, impact, and bending strengths, high thermal deformation and thermal decomposition temperatures, resistance to UV irradiation and good electrical properties.
In order to form a successful molding resin on a commercial scale, a polymer should be capable of being molded conveniently without significant degradation in physical properties. In this respect, although the aforementioned aromatic polyesters generally display excellent physical and chemical properties, a persistent and troublesome problem has been their sensitivity to hydrolytic degradation at elevated temperatures. This is demonstrated by the loss of tensile strength which can occur when an aromatic polyester resin is molded and subsequently immersed in boiling water. This tendency may be explained, in part, by the hydrolysis of the ester linkages under these conditions. In any event, it is to be appreciated that sensitivity to moisture represents a significant problem in aromatic polyester resins that would significantly limit their commercial utility in applications such as in autoclaves or an elevated temperatures in humid atmospheres.
Accordingly, it is a principal object of this invention to prepare aromatic polyester compositions having superior physical and chemical properties as well as improved hydrolytic stability.